The present disclosure generally relates to methods for improving adhesion between a metal and a polymeric material, and more particularly to improving chemical and/or mechanical adhesion between a shape memory alloy and the polymeric material.
Applications of shape memory alloys (SMA) can include embedding of the SMA material into a polymer material composite to control external shape, change stiffness, and provide vibration control of the composite, for example. The performance of applications comprising SMA material embedded in a polymeric material is heavily dependent on the quality of the SMA-polymer adhesion. The interface must have sufficient adhesion to transfer the stresses and strains from the SMA constituents to the surrounding material; the stronger the adhesion, the higher level of strain that can be transferred prior to mechanical failure. An exemplary use would be an automotive component with numerous SMA wires embedded in a polymeric material. The embedded wires must remain adhered to the polymeric material when they are deformed, for example, by application of an external current.
One method for improving adhesion between the SMA and the polymer involves treating the surface of the SMA with silane coupling agents prior to bonding the SMA to a reactive polymeric material, for example, an epoxy resin. However, the use of silane coupling agents can produce toxic compounds. Additionally, the silane coupling agents must be hydrolyzed before use, and the hydrolyzed solutions have a very finite stable lifetime. Moreover, adhesion quality needs to be improved for certain applications. Another approach involves hand sanding or sandblasting the SMA material. However, as the size of the SMA used in an application decreases to micron- or nano-sized particles, sanding or sandblasting treatments become difficult and not suitable.
Accordingly, a need exists for improved methods of adhering shape memory alloys to polymeric materials.